The invention relates to a method and apparatus for analyzing samples by gas chromatography using a sampling tube.
German Patent DE 44 19 596 C1 has disclosed a thermal desorption device for a gas chromatograph with a temperature-controlled furnace which is provided with a carrier-gas connection and with an evaporator tube, the evaporator tube being an exchangeable sampling tube which can be received by a receiving chamber of the furnace and one end of which can be inserted into a receiving piece, sealed with respect to the outside by means of a seal, in which case the receiving piece has two seals, which are arranged spaced apart in the region of the casing, and can be inserted into a receptacle of corresponding design, the carrier-gas connection opening in the region of an annular gap between receptacle and receiving piece, between the two seals situated on the casing, which for its part is connected to an annular gap surrounding the inserted end of the sampling tube, with a trap connected downstream. In this case, the sampling tube may contain either a solid or volatile or semi-volatile substances adsorbed on an adsorbing agent as the sample. However, the sampling tube is not suitable for applying substances to be analyzed by gas chromatography which are contained in a liquid or liquid-vapor-laden gaseous starting sample material, since liquid contained in the starting sample material would freeze in the downstream trap and would block the gas chromatograph.
European patent application EP 0 245 642 A1 has likewise disclosed a method for sampling by means of thermal desorption using a sampling tube, in which method adsorbed substances are desorbed on a capillary column of a gas chromatograph by means of a carrier gas via an injector containing the sampling tube.
The object of the invention is to provide a method and sampling tube which make it possible to analyze substances originating from liquid or liquid-vapor-laden gaseous starting sample material with as little loss as possible and without freezing.